Company email (January 2015):
Q: "I was wondering if you would be able to tell me if your lager is suitable for vegetarians and or vegans?"
A: "Yes it is"

Company email (March 2014):
"Bacon was used in the kettle while we brewed the beer so Lumberjack is one of our few beers that is not suitable for vegetarians."

Note from Sian and company email (March 2014):
"Update for you on Brewdog beers: their Lumberjack Breakfast Stout was brewed using bacon (I have no idea how!). They weren't advertising the fact it wasn't vegetarian when I was in their Manchester bar a few days ago -- the bartender just casually mentioned it after I'd already tried some! -- but they're going to contact all their bars and remind them to make it clear in future.

I also double-checked if they had any other beers which weren't vegetarian or vegan, and they said:
All our core range is vegan and vegetarian friendly and the only beer we produce regularly that is not vegan friendly is Dogma, as it contains honey. Some of our one off and special brews sometimes contain ingredients like lactose or honey but these are included on bottle labels and should be displayed in our bars."